Method of fabricating semiconductor chip assemblies

ABSTRACT

A method of making a microelectronic package includes providing a first microelectronic element having electrically conductive parts and including first and second surfaces and providing a compliant element including a releasable adhesive over the first surface of the first microelectronic element. A second microelectronic element having electrically conductive parts is abutted against the releasable adhesive so that the second microelectronic element is releasably assembled to the first microelectronic element and the electrically conductive parts of the first and second microelectronic elements are connected to one another. The releasably assembled package is tested to determine whether the package has been properly assembled. A curable liquid is then introduced between the first and second microelectronic elements of a properly assembled package and the curable liquid is cured to permanently assemble the first and second microelectronic elements together.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation-in-part of U.S. patentapplication Ser. No. 08/610,610 filed on Mar. 7, 1996, now U.S. Pat. No.5,834,339, and a continuation-in-part of U.S. Ser. No. 08/658,577 filedJun. 5, 1996, now U.S. Pat. No. 5,875,545 and claims the benefit of U.S.Provisional Application No. 60/032,722 filed on Dec. 13, 1996, and isrelated to commonly assigned U.S. patent application Ser. No. 08/726,697filed on Oct. 7, 1996, now U.S. Pat. No. 5,776,796, the disclosures ofwhich are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates generally to the art of electronicpackaging and more specifically relates to methods of making compliantsemiconductor chip packages.

BACKGROUND OF THE INVENTION

Modern electronic devices utilize semiconductor chips, commonly referredto as “integrated circuits” that incorporate numerous electronicelements. These chips are typically mounted on substrates, such asprinted circuit boards, which physically support the chips andelectrically interconnect each chip with other elements of the circuit.The substrate may be a part of a discrete chip package used tointerconnect a single chip to external circuits or may be a “module”whereby one or more chips are mounted directly to a substrate whichinterconnects the chips with other circuit elements mounted to thesubstrate. In either case, the semiconductor chip(s) must be securelyassembled with the substrate and must have reliable electricalinterconnection(s) to the substrate.

Advanced semiconductor chips may require hundreds of input/output(“I/O”) connections and the substrate must accommodate all of therequired external electrical interconnections to the chip. Structuresconnecting the chip to the substrate ordinarily are subject tosubstantial strains caused by thermal cycling as temperatures within thechip package change during operation. Typically, the chip and thesubstrate expand and contract by different amounts. This causes theelectrical contacts on the chip to move relative to the electricalcontact pads on the substrate, thus deforming the electricalinterconnections between the chip and substrate and placing them undermechanical stress. These repeated stresses can cause breakage of theelectrical interconnections.

U.S. Pat. Nos. 5,148,265 and 5,148,266, the disclosures of which arehereby incorporated by reference herein, solve these problems byproviding a flexible, sheet-like interposer including conductiveterminals and flexible leads connected to and extending from theterminals. This flexible layer is mounted over the face of asemiconductor chip, preferably with a soft, compliant material disposedbeneath the flexible layer and the terminals. The conductive terminalsare electrically connected to electrical contacts on the semiconductorchip by the flexible leads. The conductive terminals can be connected orbonded to contact pads on a substrate so as to connect the semiconductorchip to the substrate. Because the terminals are moveable with respectto the contacts on the semiconductor chip, the assembly compensates forthermal expansion. Also, because the terminals are compliant or moveablein the vertical directions normal to the face of the chip, the terminalscan be readily engaged with a test probe before assembly to thesubstrate. Thus, the subassembly can be tested prior to assembly to thesubstrate.

Commonly assigned U.S. Pat. No. 5,548,091, the disclosure of which ishereby incorporated by reference herein, discloses a prefabricatedinterposer or connection component for a semiconductor chip. Theconnection component includes a flexible dielectric film having top andbottom surfaces and further includes conductive terminals accessible ata surface of the dielectric film and flexible leads extending from theterminals. The connection component further includes an adhesivedisposed on the bottom surface of the flexible dielectric film forbonding the bottom surface of the dielectric film to the semiconductorchip. The adhesive desirably is solid and non-tacky at temperaturesbelow a preset activation temperature, but is adapted to reach aflowable condition upon heating to above the preset activationtemperature, and to form a bond after such heating. Preferably, theadhesive is adapted to form a relatively weak bond to the bottom surfaceof the dielectric film or to the surface of the chip. Thus, theconnection component can be removed from a chip after bonding thereto.This greatly facilitates repair and reclaim of chips from subassemblieswhich prove to be defective when tested. Such defective subassembliesmay arise, for example, where there is a fault in the connectioncomponent or the bonding process.

For example, commonly assigned U.S. Pat. No. 5,659,952, the disclosureof which is hereby incorporated by reference herein, discloses a methodof fabricating a compliant interface for a semiconductor chip typicallycomprised of a compliant encapsulation layer having a controlledthickness. In certain preferred embodiments of the '952 Patent, aconnection component, such as a flexible, substantially inextensibledielectric film, is provided. A compliant element, such as a pluralityof compliant pads defining channels therebetween, is attached to a firstsurface of the first support structure. The compliant pad/connectioncomponent subassembly is then assembled with a semiconductor chip havinga front face including a plurality of contacts. During assembly, thefront face of the semiconductor chip is abutted against the compliantpads and the contacts are electrically connected to correspondingterminals on a second side of the dielectric film. A curable liquidencapsulant material, such as a curable silicone elastomer, is thenprovided between the semiconductor chip and the dielectric film andaround the compliant pads while the chip and the dielectric film areheld in place. The liquid encapsulant is then cured, whereby thecompliant pads and the cured encapsulant provide a substantiallycontinuous compliant interface between the semiconductor chip and theflexible dielectric film.

The above-referenced '697 application discloses a method ofencapsulating a semiconductor chip package. According to preferredembodiments of the '697 application, a semiconductor chip packageassembly has a compliant element or spacer layer between the top surfaceof a flexible dielectric film and the contact bearing surface of asemiconductor chip. The flexible dielectric film has conductive leadsthereon, the leads having first ends which are electrically connected tothe terminals and second ends which are bonded to the respective chipcontacts. A protective layer is attached on a bottom surface of thedielectric film to cover the terminals on the substrate and to seal anyapertures in the dielectric film. After attachment of the protectivelayer, a flowable, curable encapsulant material is deposited around atleast a portion of a periphery of the semiconductor chip so as toencapsulate the conductive leads. The protective layer prevents thecurable encapsulant from flowing through any dielectric film apertures.The encapsulant material is then cured or at least partially cured toallow for handling and/or further processing.

SUMMARY OF THE INVENTION

One aspect of the present invention provides a method of making amicroelectronic package. The method includes providing a firstmicroelectronic element having electrically conductive parts andincluding a first surface and a second surface. The firstmicroelectronic element preferably includes a flexible dielectric filmhaving conductive terminals accessible at one or more surfaces thereofand flexible leads integrally connected to the conductive terminals andextending therefrom. A compliant element, such as a silicone elastomer,is preferably provided over the first surface of the firstmicroelectronic element. The combination of the first microelectronicelement and the compliant element is hereinafter referred to as the“package subassembly.” The compliant element preferably includes a“releasable adhesive,” i.e., an adhesive material which is capable of atleast temporarily securing two or more microelectronic elements togetherso that the elements will remain together, but so that the elements canbe separated from one another deliberately without destroying theelements.

In certain preferred embodiments, a second microelectronic elementhaving electrically conductive parts is provided. The secondmicroelectronic element preferably includes a semiconductor chip havinga front face including electrical contacts on a peripheral region of thefront face. The second microelectronic element is abutted against thereleasable adhesive so that the second microelectronic element isreleasably assembled to the first microelectronic element. For example,when the second microelectronic element is a semiconductor chip, thechip is preferably assembled with the package subassembly by abuttingthe front face of the semiconductor chip against the releasableadhesive. Thus, the first and second microelectronic elements form areleasably assembled package. The package may be tested and evaluatedbefore the elements are permanently assembled together. If thereleasably assembled chip package fails any one of a number of teststhen the releasable adhesive allows the relatively expensivemicroelectronic elements of the package, such as a semiconductor chip,to be easily disassembled from the package and reassembled with othermicroelectronic elements or package subassemblies. The bond created bythe releasable adhesive is relatively weak so that the chip can beremoved from the package subassembly without destroying the chip orrendering the chip useless. The releasable adhesive may include amaterial selected from the group consisting of pressure-sensitiveadhesives, thermoplastics and polyimide siloxane adhesives. In certainembodiments, the compliant element may completely comprise thereleasable adhesive. However, in other embodiments the compliant elementmay include a core or central region including a compliant material,such as a silicone elastomer, and one or more exterior surface regionsincluding the releasable adhesive. Most preferably the releasableadhesive is provided at a surface of the compliant element which isremote from the first microelectronic element. The remote surface of thecompliant element is further defined below as the surface which ispreferably abutted against the second microelectronic element.

After the first microelectronic element and the compliant elementincluding the releasable adhesive have been assembled together, theresulting package subassembly may be stored prior to assembly with thechip or other second microelectronic element. The package subassembly ispreferably prepared for storage by providing a release liner, such as arelatively thin, flexible plastic sheet, over the releasable adhesive atthe remote surface of the compliant element. The release liner mayinclude a release treatment such as the synthetic flourine-containingresin commonly sold under the trademark Teflon®, at one or more surfacesthereof, so that, when necessary, the release liner may be readilyremoved from the compliant element to expose the releasable adhesive.Package subassemblies manufactured according to this particularpreferred embodiment may be fabricated at one location, placed instorage and then shipped to remote manufacturing facilities for chip ordie attach processes.

In certain preferred embodiments, after the first and secondmicroelectronic elements have been releasably assembled together, theelements are electrically connected to one another by bonding theflexible leads of the first microelectronic element to the electricalcontacts of the second microelectronic element. The microelectronicpackage is then tested and evaluated to determine whether the package isoperating properly and to uncover any damage and/or defects in thepackage. Common defects typically include misalignment of the contactsof the second microelectronic element with respect to the flexible leadsof the first microelectronic element and/or misalignment of thecompliant element over the first surface of the first microelectronicelement. As such, one portion of the test may include an inspection toassure that the electrically conductive parts of the first and secondmicroelectronic elements are in substantial alignment with one another.Another portion of the test may include engaging the electricallyconductive parts of the first microelectronic element with a test probeto determine whether the electrically conductive parts of the first andsecond microelectronic elements have been properly interconnected. Iftesting uncovers a defect in the package after the leads have beenbonded to the chip contacts, the flexible leads may be broken and thelead remnants/package subassembly removed so that the secondmicroelectronic element may be reused on another package subassembly.The testing step may precede the step of electrically interconnectingthe first and second microelectronic elements or may be conducted afterthe first and second microelectronic elements have been electricallyinterconnected.

The utiliation of a releasable adhesive for releasably assembling thesecond microelectronic element with the package subassembly makes itpossible to test and evaluate the operability of the package before thesecond microelectronic assembly is permanently assembled to the packagesubassembly. As a result, a manufacturer may selectively remove ordisassemble the second microelectronic element from the microelectronicpackage subassembly if any defects are discovered during testing andevaluation of the packages. As a result, operationally soundmicroelectronic elements (i.e. “good” semiconductor chips) may bereclaimed from defective packages without destroying the integrity ofthe chips so that the chips may be reassembled with other fullyoperational package subassemblies. This particular benefit can result insubstantial cost savings because complex microelectronic elements, suchas semiconductor chips, are relatively expensive in comparison to theother elements of the microelectronic package (e.g. the flexibledielectric film).

After the releasably assembled package has passed the tests describedabove, the first and second microelectronic elements may be permanentlyassembled together by using a “lock-down” encapsulant. The “lock-down”encapsulant preferably includes a curable liquid material such as acurable silicone elastomer. Before the liquid encapsulant is introduced,a protective coverlay is preferably provided over the second or exteriorsurface of the first microelectronic elements to isolate and protect theconductive terminals from the curable liquid encapsulant so that theterminals are not covered by the curable liquid and remain accessibleafter this stage of the assembly process. The curable liquid encapsulantis then provided between the first and second microelectronic elementsand around the compliant element. The liquid encapsulant preferablysurrounds the compliant element and those portions of the electricallyconductive parts lying between the first and second microelectronicelements. In further preferred embodiments, a second protective coverlaymay be provided over the rear surface of the second microelectronicelement to prevent the curable liquid encapsulant from coming in contactwith the rear surface thereof. The second protective coverlay ispreferably substantially similar to the first protective coverlay. Thecurable liquid encapsulant may then be cured to permanently assemble thefirst and second microelectronic elements. The cured liquid encapsulantand the compliant element preferably provide a continuous, uniform,compliant layer between the first and second microelectronic elements.The cured encapsulant and the compliant element are preferably CTEmatched and comprise materials which are substantially similar, i.e.silicone elastomer.

After the curable liquid encapsulant has been cured, the curedencapsulant layer may be severed outside the perimeter of the secondmicroelectronic element to provide an individual microelectronic packagehaving a compliant bumper. The protective coverlays may be maintained inplace while the package is in storage to protect the package fromcontamination. Preferably, the protective coverlay over the exteriorsurface of the first microelectronic element is maintained in placewhile the package is in storage in order to isolate the conductiveterminals from contaminants. When it is desirable to electricallyconnect the permanently assembled microelectronic package with anexternal circuit element, such as a printed circuit board, theprotective coverlay may be removed from the exterior surface of thefirst microelectronic element to expose the conductive terminals so thatthe conductive terminals may be electrically interconnected withcontacts on the external circuit element.

In other preferred embodiments, the compliant element may include aplurality or array of compliant pads, whereby the compliant pads definechannels running between any two adjacent pads. The compliant padspreferably include the releasably adhesive, most preferably at one ormore surface regions thereof. When the curable liquid encapsulant isprovided between the first and second microelectronic elements, theliquid encapsulant flows through the channels between the compliantpads. After the liquid encapsulant has been cured, the cured encapsulantand the compliant pads provide a continuous and uniform compliant layerbetween the first and second microelectronic elements.

In other preferred embodiments of the present invention, a method ofmaking a plurality of microelectronic packages includes providing aplurality of first microelectronic elements, such as the flexibledielectric sheet described above, having electrically conductive partsand including first and second surfaces. A plurality of compliantelements are then provided over the first surfaces of the firstmicroelectronic elements. Each compliant element includes a releasableadhesive at a surface remote from the first microelectronic element. Aplurality of second microelectronic elements, such as the semiconductorchips described above, are then provided and abutted against thereleasable adhesive so that the second microelectronic elements contactthe releasable adhesive of the compliant element and are releasablyassembled with the first microelectronic elements. The first and secondmicroelectronic elements are then electrically interconnected with oneanother. The resulting plurality of microelectronic packages are thentested and evaluated using the techniques described above. As mentionedabove, testing of the packages may occur before or after the pluralityof first and second microelectronic elements have been electricallyinterconnected with one another, or both before and after suchelectrical interconnection. During testing, the releasably assembledpackages are evaluated to identify properly and improperly assembledpackages. Preferably, the first and second microelectronic elements ofany improperly assembled packages are disassembled so that the secondmicroelectronic elements may be reclaimed. The reclaimed secondmicroelectronic elements may then be reassembled with other packagesubassemblies to provide reassembled microelectronic packages. Thereassembled packages are then electrically interconnected and re-testedto determine whether they are properly or improperly assembled. Acurable liquid is then provided between the first and secondmicroelectronic elements of the properly assembled packaged and thecurable liquid is cured so that the first and second microelectronicelements are permanently assembled to one another.

These and other objects, features and advantages of the presentinvention will be more readily apparent from the detailed description ofthe preferred embodiment set forth below and when taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a fragmentary sectional view of a microelectronic packageduring one stage of an assembly method in accordance with preferredembodiments of the present invention.

FIGS. 1B through 1H show the microelectronic package of FIG. 1A duringfurther stages of an assembly process in accordance with preferredembodiments of the present invention.

FIG. 2A shows a fragmentary sectional view depicting a microelectronicpackage during one stage of an assembly process in accordance withfurther embodiments of the present invention.

FIG. 2B shows the microelectronic package of FIG. 2A during furtherstages of an assembly process in accordance with preferred embodimentsof the present invention.

FIG. 3A shows a fragmentary sectional view depicting a microelectronicpackage during an assembly process in accordance with still furtherembodiments of the present invention.

FIG. 3B shows the microelectronic package of FIG. 3A during furtherstages of an assembly process in accordance with preferred embodimentsof the present invention.

FIG. 4. shows a fragmentary sectional view of a microelectronic packagein accordance with yet further embodiments of the present invention.

FIG. 5 shows a microelectronic package in accordance with still furtherembodiments of the present invention.

FIG. 6A shows a fragmentary side view of a method of making a pluralityof microelectronic packages according to another embodiment of thepresent invention.

FIG. 6B shows the microelectronic packages in FIG. 6A during a furtherstage of the assembly process.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

One aspect of the present invention provides a method of making amicroelectronic package. Referring to FIG. 1A, a first microelectronicelement 20 includes a flexible sheet-like dielectric film having a firstsurface 22 and a second surface 24. The terms “first” and “second” areused herein to indicate directions relative to the structure of thepackage itself. It should be understood that these terms are used torefer to the frame of reference of the package, and not to the ordinary,gravitational frame of reference. Likewise, the terms “front” and “rear”should also be understood as referring to the frame of reference of thecomponent itself. The dielectric film 20 is preferably formed from apolymeric material such as polyimide having a typical thickness ofapproximately between 25 to 75 microns. The dielectric film 20 hasconductive terminals 26 accessible at the second surface 24 thereof andelectrical parts or flexible leads 28 integrally connected to andextending from the conductive terminals 26. The conductive terminals 26and the flexible leads 28 are preferably defined using photolithographictechniques whereby a single sheet of copper is attached to the firstsurface 22 of the flexible dielectric film 20, such as by usinglamination, electroplating or sputtering processes. The flexible leads28 are preferably configured to be releasably detachable from theflexible dielectric film 20, such as described in commonly assigned U.S.Pat. Nos. 5,489,749 and 5,536,909, the disclosures of which are herebyincorporated by reference herein. The dielectric film 20 also includesbond windows 29 for accessing the flexible leads during a bondingoperation, as will be described in more detail below.

A compliant element 30, preferably comprising a silicone elastomer isprovided over the first surface 22 of the dielectric film 20. Thecompliant element 30 may be formed directly on the first surface 22 ofthe flexible dielectric film 24, such as by using the techniquesdisclosed in the aforementioned '592 Patent. The compliant element 30may also be preformed and stored separately from the flexible dielectricfilm 20 as disclosed in commonly assigned U.S. patent application Ser.No. 08/879,922, the disclosure of which is hereby incorporated byreference herein. Compliant element 30 includes a releasable adhesive 32at a surface 34 of the compliant element 30 which is remote from theflexible dielectric film 20. The releasable adhesive 32 is preferablyselected from the group consisting of pressure sensitive adhesives(“PSA”), thermoplastic materials and polyimide siloxane adhesives. Theflexible dielectric film 20 and the compliant element 30 including thereleasable adhesive 32 form a microelectronic package subassembly 36(hereinafter referred to as the “package subassembly”) which may beplaced in storage, or shipped to another location before being assembledwith another microelectronic element. A flexible release liner 38 ispreferably provided over the releasable adhesive 32 before the packagesubassembly 36 is placed in storage in order to isolate the releasableadhesive 32 from contaminants.

Referring to FIG. 1B, before the package subassembly 36 is releasablyassembled to a second microelectronic element, such as a semiconductorchip (not shown), the release liner 38 is removed to expose thereleasable adhesive 32. Prior to peeling off the release liner 38, heatmay be applied to the exterior surface 40 of the release liner 38 toreduce the level of adhesion between the release liner 38 and thereleasable adhesive 32, thereby insuring that the compliant element 30will remain on the flexible dielectric film 20. After heat has beenapplied to the release liner 38, the flexible release liner 38 shouldpreferably be pulled at a severe angle of departure which furtherinsures that the compliant element 30 remains on the first surface 22 ofthe flexible dielectric film 20. A surface treatment 42, such as asynthetic fluorine containing resin sold under the trademark Teflon®,may also be provided at one or more surfaces of the release liner 38 tofurther reduce the level of adhesion between the release liner 38 andthe releasable adhesive 32. As a result, the compliant element 30 willremain on the first surface 22 of the flexible dielectric film 20 whenthe release liner 38 is removed.

Referring to FIG. 1C, after the release liner 38 has been removed fromthe compliant element 30 to expose the releasable adhesive 32, thepackage subassembly 36 is juxtaposed with a second microelectronicelement 44, such as a semiconductor chip. The semiconductor chip 44 hasa generally planar front face 46 including electrical parts or contacts48 formed on peripheral regions thereof. With the particular chip shown,the contacts 48 are generally arranged in rows (not shown) which areadjacent and run parallel to each edge of the chip 44. The contacts 48in each row are spaced at very close intervals, typically about 100 toabout 250 micrometers center-to-center.

Referring to FIG. 1D, the semiconductor chip 44 is releasably assembledwith the package subassembly 36 by abutting the front face 46 of thesemiconductor chip 44 against the releasable adhesive 32 so that thecontacts 48 of the semiconductor chip 44 are aligned with the bondwindows 29 and the flexible leads 28 of the flexible dielectric film 20.Alignment of the contacts 48 with the bond window 29 and flexible leads28 facilitates electrical connection of the flexible leads 28 with thecontacts 48, as will be described in more detail below. The releasablyassembled package is then tested and/or evaluated to determine whetherthe package has been properly or improperly assembled and/or to identifyany defects. Common defects in the package may include misalignment ofthe chip contacts 48 with respect to the flexible leads 28 ormisalignment of the compliant element 30 between the flexible dielectricfilm 20 and the semiconductor chip 44. As will be discussed in moredetail below, another problem may include improper electrical connectionof the chip 44 and the conductive terminals 26 of the dielectric film20.

Referring to FIGS. 1E and 1F, the flexible leads 28 are then detachedand bonded to the contacts 48 on the front face 46 of the semiconductorchip 44 such as by using ultrasonic or thermosonic bonding techniquesconventionally known in the art or by using the various bondingtechniques disclosed in U.S. Pat. Nos. 5,398,863; 5,390,844; 5,536,909and 5,491,302. The bonding of the flexible leads 28 to their respectivechip contacts 48 provides some mechanical strength to the package sothat the releasable adhesive 32 does not peel off or delaminate from thefront face 46 of the semiconductor chip 44 and/or the flexibledielectric film 20. However, as described below, the semiconductor chip44 can still be nondestructively removed from the releasable adhesive 32of the compliant element 30 after the flexible lead bonding operation bybreaking the leads 28. The electrical connections of the package may betested by engaging the terminals 26 of the flexible dielectric film 20with test probes (FIG. 6A) to assure that the flexible leads 28 of theflexible dielectric film 20 are properly connected to the contacts 48 ofthe semiconductor chip 44.

If testing identifies an improperly assembled or defective semiconductorchip package, then the semiconductor chip 44 may be disassembled fromthe package subassembly 36 and reassembled with another packagesubassembly. The releasable adhesive 32 enables the semiconductor chip44 to be readily removed from a defective package and transferred toanother package. Preferably the chip 44 will be disassembled before theflexible leads 28 are bonded to the contacts 48. However, if the defectsin the package are not discovered until after the flexible leads 28 havebeen bonded to the chip contacts 48, the flexible leads 28 may be brokenpr pulled away from chip contacts 48 and the leads 28 and packagesubassembly 36 may be removed so that the chip 44 may be reassembledwith another package subassembly 36.

After testing and evaluation of the chip package 58 discloses that thepackage subassembly 36 and the chip 44 have been assembled withinacceptable tolerances and that none of the microelectronic elements aredefective, the semiconductor chip 44 and the flexible dielectric film 20may be permanently assembled together by adding a curable liquidencapsulant 50 around the edges of the chip package 58 and curing theencapsulant. The cured encapsulant mechanically connects and/or locksthe semiconductor chip 44 and the flexible dielectric film 20 togetherso that the compliant element 30 cannot be easily removed from thesemiconductor chip 44 and/or the flexible dielectric film 20.

Referring to FIG. 1F, a curable liquid encapsulant 50, such as a liquidsilicone elastomer, is provided between the semiconductor chip 44 andthe flexible dielectric film 20. Before the curable liquid 50 isintroduced, a first protective coverlay 52 is preferably provided overthe second surface 24 of the flexible dielectric film 20 to cover thebond windows 29 so as to prevent the curable liquid 50 from passingthrough the bond windows 29 and contacting the conductive terminals 26at the second surface 24 of the flexible dielectric film 20. A secondprotective coverlay 54 may also be provided over the rear surface 56 ofthe semiconductor chip 44 to prevent the curable liquid 50 from comingin contact with the rear surface 56. After the first and secondprotective coverlays 52 and 54 have been provided over the respectiveexterior surfaces of the semiconductor chip 44 and the dielectric film20, the curable liquid encapsulant 50 is allowed to flow between thesemiconductor chip 44 and the dielectric film 20 and around the flexibleleads 28. The curable liquid encapsulant 50 is then cured using energysuch as heat or ultraviolet light. The encapsulant 50 is preferably CTEmatched with the compliant element 30 so as to minimize the effects ofthermal cycling. The encapsulant preferably comprises the same materialas the compliant element 30, i.e., a silicone elastomer material. Thecured encapsulant 50 provides a substantially continuous compliant layerbetween the flexible dielectric film 20 and the semiconductor chip 44.

Referring to FIGS. 1F and 1G, the cured encapsulant 50 as well as thefirst and second protective coverlays 52 and 54 and the dielectric film20 may be severed outside the periphery of the semiconductor chip 44along the axis designated A—A. Severing the cured encapsulant layer 50outside the periphery of the semiconductor chip 44 provides themicroelectronic package 44 with a protective bumper 56 around theperiphery thereof. The first protective coverlay 52 may be maintained inplace over the conductive terminals 26 accessible at the second surface24 of the dielectric film 20 while the package 58 is in storage. Thesecond coverlay 54 may also remain in place for additional protection.As shown in FIG. 1H, when it is desirable to electrically connect themicroelectronic package 58 with an external circuit element 60 such as aprinted circuit board, the first protective coverlay 52 may be removedto expose the conductive terminals 26. The package 58 may then beelectrically connected to the external circuit element 60. Theconductive terminals 26 of the microelectronic package 58 are preferablyinterconnected with contacts 62 on a first surface 64 of the externalcircuit element 60 via solder balls 66 provided therebetween.

Referring to FIGS. 2A-2B, in another embodiment of the presentinvention, the flexible dielectric film 120 and the compliant element130 comprise a microelectronic package subassembly 136 which issubstantially similar to that described above with reference to FIGS.1A-1H. In this particular preferred embodiment, the compliant element130 includes a core region 168 of a compliant material such as asilicone elastomer, a first layer of a releasable adhesive 132A providedat a surface region 134 of said compliant element 130 remote from saiddielectric film 120 and a second layer of a releasable adhesive 132Bprovided between the first surface 122 of the flexible dielectric film120 and the core region 168 of the compliant element 130. The packagesubassembly 136 includes a flexible release liner 138 provided over thefirst layer of the releasable adhesive 132A. Referring to FIG. 2B, priorto assembly with the semiconductor chip 144, the flexible release liner138 is removed to expose the first layer of the releasable adhesive132A. The semiconductor chip 144 is then abutted against the releasableadhesive 132A so that the semiconductor chip 144 and the dielectric film120 are releasably assembled together. The semiconductor chip 144 andthe dielectric film 120 are then electrically interconnected asdescribed above. After testing reveals that the semiconductor chip 144and the dielectric film 120 have been properly assembled, a curableliquid 150 is provided between the chip 144 and the dielectric film 120and the encapsulant is cured in accordance with the techniques describedabove. If a package has been improperly assembled, the compliant element130 according to this particular embodiment allows a manufacturer toselectively disassemble the compliant element 130 from the dielectricfilm 120 with a minimum amount of the compliant element material left oneither the dielectric film 120 or the chip 144. For example, if thecompliant element 130 has been misapplied or misaligned with the firstsurface 122 of the flexible dielectric film 120 during attachment, thecompliant element 130 including the first and second releasable adhesivelayers 132A and 132B may be removed therefrom and replaced with anothercompliant element 130.

The compliant element shown in FIGS. 1A-1H and 2A-2B may be maintainedseparately from the flexible dielectric film until immediately prior toassembly of the semiconductor chip with the dielectric film. Forexample, the compliant element may be transferable as described in theabove-mentioned '922 application. In the '922 application, the compliantelement is provided between first and second flexible release liners sothat the compliant element may be stored and maintained separately fromthe flexible dielectric film. Immediately prior to assembly, the firstrelease liner is removed to expose one surface of the compliant elementso that the compliant element may be assembled with the flexibledielectric film. The second release liner is then removed to exposeanother surface of the compliant element so the compliant element may beassembled with the front face of a semiconductor chip. In otherpreferred embodiments, the compliant element may be screened or stencilprinted directly onto a surface of the flexible dielectric film and thencured into a solid but compliant form as disclosed in the aforementioned'952 Patent. In still further embodiments, some of the various layerscomprising the compliant element may be stenciled, screened or depositedin a liquid form on the first surface of the flexible dielectric filmand then at least partially cured. After the compliant element has beenpartially cured, other layers, such as layers of the releasableadhesive, may then be attached thereto.

Referring to FIG. 3A, in another embodiment of the present invention,the package subassembly 236 is substantially similar to that describedabove, however, the compliant element 230 in this particular embodimentincludes a plurality or array of compliant pads as disclosed in theaforementioned U.S. Pat. No. 5,659,952, the disclosure of which ishereby incorporated by reference herein. The compliant pads 230 includethe releasable adhesive 232 provided over surfaces 234 of the compliantpads 230 which are remote from the flexible dielectric film 220. Thecompliant pads 230 preferably include a release liner 238 provided overthe releasable adhesive 232 which is removed prior to assembly of thepackage subassembly 236 with another microelectronic element. Referringto FIG. 3B, after the flexible release liner 238 has been removed, asemiconductor chip 244 is assembled with the package subassembly 236 byabutting the front face 246 of the semiconductor chip 244 against thereleasable adhesive 232 of the compliant pads 230. The flexible leads228 are then bonded to the contacts 248 of the semiconductor chip 244 toelectrically interconnect the flexible dielectric film 220 and thesemiconductor chip 244. The releasably assembled package 258 is thentested and evaluated to determine whether it has been properly assembledand to uncover any damage or defects thereto. If the package 258 isfound to be improperly assembled or defective, the semiconductor chip244 may be selectively disassembled from the flexible dielectric film220 by peeling the semiconductor chip 244 from the compliant pads 230.When testing has revealed that the package has been properly assembled,a curable liquid encapsulant 250 may be provided between the flexibledielectric film 220 and the semiconductor chip 244 as described above. Aprotective coverlay 252 over the conductive terminals 226 at the secondsurface 224 of the dielectric film 220 prevents the terminals 226 frombeing covered by the curable liquid 250 and allows the conductiveterminals 226 to remain accessible.

Referring to FIG. 4, in another preferred embodiment of the presentinvention, the microelectronic package is substantially similar to thatshown in FIGS. 3A-3B and described above. In this particular embodiment,the plurality of compliant pads 330 include a first layer 332A of areleasable adhesive between the compliant pads 330 and the front face346 of the semiconductor chip 344 and a second layer 332B of areleasable adhesive between the compliant pads 330 and the first surface322 of the flexible dielectric film 320. The first layer of thereleasable adhesive 332A allows the semiconductor chip 344 to bereleasably assembled to the dielectric film 320 so that thesemiconductor chip 340 may be reclaimed if testing shows that thepackage has been improperly assembled. The second layer 332B of thereleasable adhesive enables the compliant pads 330 to be readily removedfrom attachment to the dielectric film 320 if it is determined that thecompliant pads 330 have been improperly assembled with the dielectricfilm 320. The chip package 358 is then electrically interconnected,tested and encapsulated using the techniques described above.

Referring to FIG. 5, in yet another embodiment of the present invention,the microelectronic package includes a “fan out” chip packageembodiment. A “fan out” chip package is defined as a microelectronicpackage where the leads 428 are connected to the respective contacts 448on the semiconductor chip 444 and extend outwardly beyond the peripheryof the semiconductor chip 444 to terminals 426 which are located beyondthe periphery of the chip 444. In contrast, a “fan in” chip package isgenerally defined as a microelectronic package wherein the flexibleleads are connected to the chip contacts and extend inwardly over theface of the semiconductor chip toward the conductor terminals. In theparticular “fan out” package shown in FIG. 5, the flexible dielectricfilm 420 and the compliant element 430 are attached to a stiffener plateor ring 468 having an aperture 470 in the center thereof and thesemiconductor chip 444 is disposed in the aperture 470. The compliantelement 430 includes a releasable adhesive 432 remote from the firstsurface 422 of the dielectric film 420 so that the ring 468 may bereleasably assembled with the dielectric film 420. The “fan out” chippackage is then electrically interconnected, tested and encapsulated asdescribed above.

Still further preferred embodiments of the present invention providemethods of making a plurality of microelectronic packages, whereby theassembly methods utilized are substantially similar to those describedabove. Referring to FIGS. 6A and 6B, in one particular embodiment, aplurality of semiconductor chips 544A, 544B and 544C are provided on asupporting element 572. The semiconductor chips 544A, 544B and 544C arearranged with the rear surfaces 574 thereof in contact with a topsurface 576 of the supporting element 572. Package subassemblies 544A,544B and 544C, substantially similar to those described above, are thenabutted against the front faces 546 of the semiconductor chips 544A,544B and 544C so that the chips and package subassemblies are releasablyassembled with one another. The flexible leads 528 of each packagesubassembly are then bonded to the contacts 548 of the chips associatedtherewith in order to electrically interconnect the chip and thedielectric film 520. The plurality of microelectronic packages are thentested and evaluated in accordance with the parameters outlined above.One such test (shown in FIG. 6A) includes engaging the conductiveterminals 526 of the releasably assembled packages with a set of testprobes 578 to evaluate the electrical interconnections between the chipsand the dielectric films. Referring to FIG. 6B, after testing, thepackage subassemblies of any defective packages are peeled from thesemiconductor chip so that the chip may be reclaimed and reassambledwith another package subassembly. In FIG. 6B, the package including themiddle semiconductor chip 544B was found to be defective and/orimproperly assembled. As such, the defective package subassembly 536Bwas peeled from the chip 544B so that the chip 544B could be reassembledwith another package subassembly 536B. A curable liquid (not shown) maythen be provided between the first and second microelectronic elementsof the properly assembled packages (i.e. the packages including chips544A and 544C) and the curable liquid cured so that the respective chips544A, 544C and package subassemblies 536A, 536C are permanentlyassembled to one another.

These and other variations and combinations of the features discussedabove can be utilized without departing from the present invention asdefined by the claims. For example, in other preferred embodiments ofthe present invention, the microelectronic package may comprise a “fanin/fan out” chip package wherein the flexible leads are connected torespective chip contacts and the flexible leads extend both inwardlyover the face of the chip to conductive terminals and outwardly beyondthe periphery of the chip to conductive terminals located outside theperiphery of the chip. In other embodiments, the releasable adhesive atone or more surface regions of the compliant element may include thecompliant element material itself, i.e. an uncured or partially curedregion of the compliant element. As such, the foregoing description ofthe preferred embodiments should be taken by way of illustration ratherthan by way of limitation of the claimed invention.

What is claimed is:
 1. A method of making a microelectronic package comprising the steps of: providing a first microelectronic element having first and second surfaces; providing a compliant element including a releasable adhesive over said first surface of said first microelectronic element; providing a second microelectronic element; releasably securing said first and second microelectronic elements together by abutting said second microelectronic element against said releasable adhesive so that said second microelectronic element is releasably adhered in assembled relationship to said first microelectronic element to form a releasably assembled package; testing said releasably assembled package; providing a curable liquid between said first and second microelectronic elements and around said compliant element while said first and second microelectronic elements remain releasably secured together by said releasable adhesive; and curing said curable liquid so as to permanently assemble said first and second microelectronic element after said testing step, whereby said releasable adhesive permits the separation of said first microelectronic element from said second microelectronic element prior to said curing step.
 2. A method as claimed in claim 1, wherein said first and second elements have electrically conductive parts, said method further comprising electrically interconnecting said electrically conductive parts of said first and second microelectronic elements.
 3. A method as claimed in claim 2, wherein the testing step precedes the electrically connecting step.
 4. A method as claimed in claim 3, the testing step including the step of assuring that the electrically conductive parts of said first and second microelectronic elements are in substantial alignment with one another.
 5. A method as claimed in claim 2, wherein the testing step follows the electrically connecting step.
 6. A method as claimed in claim 5, the testing step including the step of electrically testing said releasably assembled package by engaging said electrically conductive parts of said first microelectronic element with test probes.
 7. A method as claimed in claim 1, wherein said curable liquid includes a silicone elastomer.
 8. A method as claimed in claim 1, wherein said curing step includes the step of using heat or ultraviolet light.
 9. A method as claimed in claim 2, wherein said electrically connecting step includes the step of bonding said electrically conductive parts of said first and second microelectronic elements together.
 10. A method as claimed in claim 1, wherein said releasable adhesive includes a partially cured or uncured region of said compliant element.
 11. A method as claimed in claim 1, wherein said releasable adhesive includes a material selected from the group consisting of pressure sensitive adhesives, thermoplastics and polyimide siloxane adhesives.
 12. A method as claimed in claim 11, wherein said compliant element includes a plurality of compliant pads defining channels therebetween.
 13. A method as claimed in claim 12, wherein the providing a curable liquid step includes the step of allowing said curable liquid to flow through said channels.
 14. A method as claimed in claim 13, wherein said curable liquid and said compliant pads provide a continuous compliant layer after the curing step.
 15. A method as claimed in claim 1, wherein said compliant element completely comprises said releasable adhesive.
 16. A method as claimed in claim 1, wherein said compliant element comprises a core region of compliant material and one or more surface regions including said releasable adhesive.
 17. A method as claimed in claim 16, wherein said compliant material includes a silicone elastomer.
 18. A method as claimed in claim 1, wherein the providing said compliant element step includes the steps of: providing a flexible liner over said releasable adhesive at a surface of said compliant element remote from said first microelectronic element; and removing said flexible liner before the abutting step to expose said releasable adhesive.
 19. A method as claimed in claim 18, wherein said flexible liner includes a release treatment at one or more surfaces thereof.
 20. A method as claimed in claim 19, wherein said release treatment includes a synthetic flourine-containing resin.
 21. A method as claimed in claim 2, said first microelectronic element comprising a flexible dielectric film and said electrically conductive parts of said first microelectronic element including terminals accessible at an exterior surface of said package and flexible leads extending from said terminals, said step of providing said curable liquid being performed so that said terminals are not covered by said curable liquid and remain accessible.
 22. A method as claimed in claim 21, further comprising the step of providing a protective coverlay over said terminals accessible at said exterior surface of said package so as to isolate said terminals from said curable liquid during the providing a curable liquid step.
 23. A method as claimed in claim 22, wherein said protective coverlay includes a flexible sheet.
 24. A method as claimed in claim 2, wherein said second microelectronic element includes a semiconductor chip having a front face and said electrically conductive parts of said second microelectronic element include contacts on said front face of said semiconductor chip.
 25. A method of making a semiconductor package comprising the steps if: providing a connection component including a flexible dielectric film having a first surface and a second surface, said dielectric film including conductive terminals accessible at one of said surfaces thereof and flexible leads extending from said conductive terminals; providing a compliant element over said first surface of said dielectric film, said compliant layer including a releasable adhesive at a surface thereof remote from said first surface of said dielectric film; providing a semiconductor chip having a front face including contacts; releasably securing said semiconductor chip to said connection component by abutting said front face of said semiconductor chip against said releasable adhesive so that said semiconductor chip is releasably adhered in assembled relationship to said connection component to form a releasably assembled semiconductor package; connecting said flexible leads and said contacts for electrically interconnecting said semiconductor chip and said connection component; testing said releasably assembled semiconductor package; providing a curable liquid between said semiconductor chip and said connection component and around said compliant element while said semiconductor chip and said connection component remain releasably secured together by said releasable adhesive; and curing said curable liquid so that said semiconductor chip is permanently assembled with said connection component after said testing step, whereby said releasable adhesive permits the separation of said semiconductor chip from said connection component prior to said curing step.
 26. A method as claimed in claim 25, wherein the testing step precedes the connecting step.
 27. A method as claimed in claim 26, the testing step including the step of assuring that the flexible leads of said connection component are in substantial alignment with said contacts of said semiconductor chip.
 28. A method as claimed in claim 25, wherein the testing step follows the electrically connecting step.
 29. A method as claimed in claim 28, the testing step including the step of electrically testing said releasably assembled package by engaging said conductive terminals of said connection component with a test probe.
 30. A method as claimed in claim 25, wherein said curable liquid includes a silicone elastomer.
 31. A method as claimed in claim 25, wherein said curing step includes the step of using heat or ultraviolet light.
 32. A method as claimed in claim 25, wherein said connecting step includes the step of bonding said flexible leads to said contacts of said semiconductor chip.
 33. A method as claimed in claim 25, wherein said releasable adhesive includes a material selected from the group consisting of pressure sensitive adhesives, thermoplastics and polyimide siloxane adhesives.
 34. A method as claimed in claim 33, wherein said compliant element includes a plurality of compliant pads defining channels therebetween.
 35. A method as claimed in claim 34, wherein the providing a curable liquid step includes the step of allowing said curable liquid to flow through said channels.
 36. A method as claimed in claim 35, wherein said curable liquid and said compliant pads provide a continuous compliant layer after said curing step.
 37. A method as claimed in claim 25, wherein said compliant element completely comprises said releasable adhesive.
 38. A method as claimed in claim 25, wherein said compliant element comprises a core region of compliant material and one or more surface regions including said releasable adhesive.
 39. A method as claimed in claim 38, wherein said compliant material includes a silicone elastomer.
 40. A method as claimed in claim 25, wherein the providing said compliant element step includes the steps of: providing a flexible liner over said releasable adhesive at a surface of said compliant element remote from said flexible dielectric film; and removing said flexible liner to expose said releasable adhesive before the abutting step.
 41. A method as claimed in claim 40, wherein said flexible liner includes a release treatment at one or more surfaces thereof.
 42. A method as claimed in claim 41, wherein said release treatment includes a synthetic flourine-containing resin.
 43. A method as claimed in claim 25, wherein said conductive terminals are accessible at said second surface of said dielectric film, said second surface being at an exterior surface of said semiconductor package, said step of providing said curable liquid being performed so that said terminals are not covered by the curable liquid and remain accessible.
 44. A method as claimed in claim 43, further comprising the step of providing a protective coverlay over said conductive terminals accessible at said exterior surface of said package before the providing a curable liquid step so as to isolate said conductive terminals from said curable liquid.
 45. A method as claimed in claim 44, wherein said protective coverlay includes a flexible sheet. 